Clinicopathological characteristics, prognostic factors, and outcomes of elderly patients with lymphoma‐associated hemophagocytic lymphohistiocytosis: A multicenter analysis

Abstract Background Lymphoma is the most common secondary cause of hemophagocytic lymphohistiocytosis (HLH) in adults. Lymphoma‐associated HLH (LA‐HLH) in the elderly population is not rare, however, little has been reported regarding clinicopathological characteristics, prognostic factors, and outcomes of LA‐HLH in the elderly population. Methods We retrospectively analyzed a multicenter cohort of elderly patients with LA‐HLH. Clinicopathological features and treatment information were collected. The impacts of baseline characteristics and treatments on survival outcomes were analyzed. Results A total of 173 elderly patients with LA‐HLH were included. Compared with young patients, elderly patients showed different clinical and laboratory features. Regarding lymphoma subtypes, B‐cell lymphoma was more common in elderly patients (elderly 61.3% vs. young 32.3%, p < 0.001) while T/NK‐cell lymphoma was more common in young patients (65.3% vs. 35.3%, p < 0.001). The median survival of elderly patients with LA‐HLH was only 92 days. The prior use of HLH therapy or etoposide‐containing HLH therapy was not associated with improved overall survival. T/NK‐cell subtype, a lower platelet count (≤53 × 109/L), a lower albumin level (≤32.1 g/L), a higher LDH level (>1407 U/L), and a higher creatinine level (>96.8 μmol/L) were independent predictors of decreased overall survival and 60‐day survival. A prognostic index was established and demonstrated to be robust in predicting the overall survival and 60‐day survival of elderly patients with LA‐HLH. Conclusions LA‐HLH in elderly patients displayed heterogeneous clinicopathological features and survival outcomes. Treatments need to be optimized to improve the outcomes of elderly patients with LA‐HLH.


| INTRODUCTION
Hemophagocytic lymphohistiocytosis (HLH) is a rare clinical syndrome characterized by overwhelmed inflammation.HLH could be classified as primary HLH and secondary HLH.Primary HLH is caused by germline genetic defects and is always present in infants and children. 1 Secondary HLH has underlying causes and is typically identified in adults.The common underlying causes of secondary HLH include malignancies, infections, and rheumatic disorders.In the context of malignancies, lymphoma is the most common type of malignancy, accounting for over 70% of cases. 2 Geographical variation in lymphoma subtypes exists in patients with lymphoma-associated HLH (LA-HLH).4][5] By contrast, in Europe and USA, large B cell lymphoma and T-cell non-Hodgkin lymphoma are the main underlying causes of LA-HLH and a significant proportion of cases of LA-HLH were Hodgkin lymphomas. 6,7The lymphoma subtypes have significant impacts on the prognosis of LA-HLH with T/NK-cell lymphoma predicting significantly worse outcomes. 6The current recommendation for treating LA-HLH is controlling hyperinflammation by HLH-directed regimens, followed by lymphoma-directed therapy. 8he majority of cases of LA-HLH are adult cases.Whether patients in different age groups show distinct clinicopathological features and outcomes remains to be determined.Little is known about LA-HLH in the elderly population.As elderly patients have more comorbidities and reduced tolerance to chemotherapy, elderly patients with LA-HLH may need a different therapeutic approach.Therefore, we retrospectively analyzed the largest cohort focusing on elderly patients with LA-HLH to date, to explore clinical features, lymphoma subtypes, prognostic features, therapy, and outcomes of LA-HLH in the elderly population.

| Study population
This study was a multicenter, retrospective study focusing on elderly patients with LA-HLH.Data on young patients were also collected for comparison purposes.Adult patients with LA-HLH diagnosed at the participating centers from 2010 to 2023 were included in this study.The inclusion criteria were as follows: (1) age ≥18 years; (2) fulfillment of five or more of the eight HLH-2004 diagnostic criteria 9 ; and (3) histopathological diagnosis of lymphoma.Primary HLH caused by germline genetic abnormalities was excluded.The lymphoma subtyping was based on the World Health Organization classification of lymphoid neoplasms.Patients >60 years were defined as elderly patients.Young patients (18 years ≤ age ≤60 years) were included for comparison with their elderly counterparts.

| Data collection
The demographic data, clinical features, and laboratory results of all patients were extracted from the patient's medical records.Demographic data were age at diagnosis and gender.Clinical characteristics include the duration of fever and the maximum temperature, the presence of splenomegaly, and the lymphoma stage at diagnosis.The subtypes of the underlying lymphoid malignancies were also collected.Laboratory parameters included hemoglobin, platelets, absolute neutrophil count, soluble CD25, ferritin, triglycerides, fibrinogen, natural killer (NK) cell activity, lactate dehydrogenase (LDH), albumin, and creatinine.The values of laboratory parameters for diagnosis of HLH and prognosis analysis were documented separately.For the parameters in the HLH-2004 diagnostic criteria, the first values that meet a lower albumin level (≤32.1 g/L), a higher LDH level (>1407 U/L), and a higher creatinine level (>96.8 μmol/L) were independent predictors of decreased overall survival and 60-day survival.A prognostic index was established and demonstrated to be robust in predicting the overall survival and 60-day survival of elderly patients with LA-HLH.
Conclusions: LA-HLH in elderly patients displayed heterogeneous clinicopathological features and survival outcomes.Treatments need to be optimized to improve the outcomes of elderly patients with LA-HLH.

K E Y W O R D S
elderly patients, hemophagocytic lymphohistiocytosis, lymphoma, overall survival the HLH-2004 criteria were obtained.For parameters included in prognosis analysis, the latest laboratory values measured before a specific HLH-directed or lymphomadirected therapy were used.When no data were available, the first value within 72 h after treatment initiation was documented.For patients who did not receive any HLH-directed or lymphoma-directed therapy, baseline laboratory parameters at the time of diagnosis of HLH were used for prognosis analysis.

| Statistical analyses
The Mann-Whitney test was used to compare the continuous variables between the two groups.Fisher's exact test or chi-square test was used for categorical variables.The survival curves were plotted by using the Kaplan-Meier method and the log-rank test was used for comparison.In prognostic analysis, we used the R package "survminer" to determine the optimal cutoffs for continuous variables including age, hemoglobin, platelets, neutrophils, albumin, creatinine, LDH, and fibrinogen.We used 1500 μg/L as the cutoff for ferritin as there were no concrete values in some cases with high ferritin levels (for example, ferritin>1500 μg/L).Univariate and multivariate Cox regression analyses were performed to find the predictors of overall survival (OS) and 60-day survival.Statistical analyses were performed using STATA/MP, version 17.0 (StataCorp LLC) and R Software, version 4.2.2.P < 0.05 was considered statistically significant.

| General data and clinical features
A total of 173 elderly patients with LA-HLH were included.A separate cohort of 251 young patients with LA-HLH was used for comparison studies.The median age was 69 years, and the male/female ratio was approximately 1.8:1 (Table 1

| Lymphoma subtypes in elderly patients with lymphoma-associated HLH
In elderly patients with LA-HLH, 106 patients had B-cell non-Hodgkin lymphoma (NHL), 61 patients had T/NKcell lymphoma, and six patients had Hodgkin lymphoma.The most common subtype was large B-cell lymphoma (56.7%, 98/173), followed by angioimmunoblastic T-cell lymphoma (AITL, 9.3%, 16/173), aggressive NK cell leukemia (ANKL, 6.4%, 11/173), extranodal NK cell lymphoma, nasal type (ENKL, 5.8%, 10/173), and peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS, 5.8%, 10/173).It is important to note that the proportion of B-cell NHL was significantly higher in elderly patients than in young patients (elderly 61.3% vs. young 32.3%, p < 0.001).And the T/NK-cell lymphoma was less common in elderly patients (35.3% vs. 65.3%, p < 0.001).Furthermore, we compared the proportions of specific subtypes between elderly and young patients.Large B-cell lymphoma was more common in elderly patients, while ANKL and ENKL were more common in younger patients than in older patients.AITL was more frequent in older patients, although the difference was only marginally significant (Table 2).

| Treatments and outcomes for elderly patients with lymphoma-associated HLH
A total of 168 elderly patients with LA-HLH had followup data and the median follow-up was 54 days.These patients were further analyzed.The treatments for these patients were summarized in Table S1.A total of 102 patients received HLH therapy as the initial treatment.Among patients who received HLH therapy, 62 patients received etoposide-containing HLH therapy.A total of 125 patients received lymphoma-directed therapy, and 50 patients received lymphoma-directed therapy directly without a prior HLH therapy.A total of 101 patients were treated with etoposide, in initial HLH-directed or lymphoma-directed therapy.Sixteen patients did not receive either HLH therapy or lymphoma-directed therapy, mostly due to the rapid progression of the disease.The median survival for elderly patients was 92 days, and the 60-day survival probability was 56.2%.No significant differences were observed in OS and 60-day survival probabilities between the elderly and younger patients (median survival: elderly 92 days vs. young 126 days, p = 0.641, Figure 1A; 60-day survival probabilities: elderly 56.2% vs. young 59.9%, p = 0.439, Figure 1B).In subgroup analysis based on lymphoma subtypes (B cell lymphoma or T/ NK cell lymphoma or Hodgkin lymphoma), the survival outcomes did not differ between the elderly and younger patients (Figure S1).Patients who did not receive either HLH therapy or lymphoma-directed therapy (n = 16) had a very dismal prognosis, with a median survival of only 4 days.Patients treated with HLH therapy and those who received lymphoma-directed therapy without prior HLH therapy showed similar OS (p = 0.510, Figure 2A) and 60-day survival probabilities (p = 0.760, Figure S2A).The use of etoposide-containing HLH therapy was not associated with improved OS (p = 0.440, Figure 2B) or 60-day survival (p = 0.410, Figure S2B).Outcomes of patients who received etoposide treatment in HLH-directed or lymphoma-directed therapy were similar to those who received lymphoma-directed therapy without any etoposide regimen (OS, p = 0.590, Figure 2C; 60-day survival, p = 0.160, Figure S2C).In patients who received lymphoma-directed therapy, the use of etoposidecontaining lymphoma-directed therapy was associated with improved overall survival, although the difference was not statistically significant (p = 0.090, Figure 2D); the use of etoposide-containing lymphoma-directed therapy was significantly associated with improved 60-day survival (p = 0.025, Figure S2D).We then separately analyzed the role of etoposide in Bcell LA-HLH and T/NK-cell LA-HLH.For B-cell LA-HLH, we found that etoposide-containing HLH therapy was not associated with improved outcomes (OS or 60-day survival, Figure S3A,D).The use of etoposide was associated with improved 60-day survival (p = 0.004, Figure S3E) but OS (p = 0.310, Figure S3B).For B-cell LA-HLH, etoposidecontaining lymphoma-directed therapy showed an advantage over lymphoma-therapy without etoposide in improving 60-day survival (p = 0.012, Figure S3F) but not OS (p = 0.140, Figure S3C).For T/NK-cell LA-HLH, etoposide-containing HLH therapy, etoposide use, or etoposide-containing lymphoma-directed therapy was not associated with improved OS or 60-day survival (Figure S3A-F).

| Prognostic factors
We analyzed potential prognostic markers for elderly patients with LA-HLH.We found that lymphoma subtypes had a significant impact on OS in elderly patients with LA-HLH (p = 0.009, Figure 3).Patients with NK-cell neoplasm had a median survival of only 21 days.In addition to lymphoma subtypes, we also analyzed the prognostic roles of age, hemoglobin, neutrophil counts, platelets, fibrinogen, LDH, ferritin, albumin, and creatinine (Table 3).The best cutoffs of age, hemoglobin, neutrophil counts, platelets, fibrinogen, LDH, albumin, and creatinine were shown in Table 3.In univariate analysis, the T/NK-cell subtype, a lower platelet count (≤53 × 10 9 /L), a lower albumin level (≤32.1 g/L), a higher LDH level (>1407 U/L), a higher creatinine level (>96.8 μmol/L), and a lower fibrinogen level (≤2.59 g/L) predicted worse OS.Further multivariate analysis demonstrated that the T/NK-cell subtype, a lower platelet count, a lower albumin level, a higher LDH level, and a higher creatinine level were independent predictors of decreased OS.The lymphoma subtype, platelets, albumin, LDH, and creatinine were also independent prognostic factors for the 60-day survival (Table S2).These five factors were used to construct a prognostic index for elderly patients with LA-HLH.Weighted risk scores of 1 were assigned to each factor and the total risk scores ranged from 0 to 5. Patients were divided into three risk groups: lowrisk (risk score: 0-1), intermediate-risk (risk score: 2-3), and high-risk (risk score: 4-5).Patients in different risk groups showed significantly different outcomes.The median survival for patients in the low-risk, intermediaterisk, and high-risk groups were not reached, 74 days, and 5 days, respectively (p < 0.001, Figure 4A).The 60-day survival probabilities for the three groups were also significantly different (high-risk 92.4% vs. intermediate-risk 50.4% vs. low-risk 5.9%, p < 0.001, Figure 4B).

| DISCUSSION
In the current study, we retrospectively analyzed a large cohort of elderly patients with LA-HLH.We found that elderly patients with LA-HLH showed different clinical characteristics and lymphoma subtypes from young patients.We found that the triggers underlying LA-HLH in elderly patients were significantly different from those in young patients.B-cell NHL was more common in elderly patients while T/NK-cell lymphoma was more common in young patients.Regarding specific subtypes, large B-cell lymphoma was much more prevalent in elderly patients with LA-HLH, while ANKL and ENKL were more common in young patients.The prognosis of elderly patients with LA-HLH was poor, and those with T/NK-cell subtypes had an extremely poor prognosis.Initial HLH therapy or Initial etoposide-containing HLH therapy did not seem to the survival of elderly patients with LA-HLH.Use of etoposide or etoposide-containing lymphoma-directed therapy was not associated improved OS of elderly patients with LA-HLH.
Identification of the triggers for secondary HLH is important for treatment decisions in patients with HLH.Understanding the lymphoma subtypes underlying HLH could be helpful for differential diagnosis in patients with secondary HLH. 3 According to most of previous studies, T/NK-cell lymphoma is more common than B-cell NHL as a trigger for HLH. 3,5,10However, these studies did not separately analyze the young and old patients.According to a previous study, the most common subtypes in children or adolescents with malignancy-associated HLH are anaplastic large cell lymphoma (ALCL) and lymphoblastic lymphoma. 11This finding suggests that the distribution of lymphoma subtypes may vary in different age groups.Our study revealed that the distribution of lymphoma subtypes was different between different age groups in adult patients with LA-HLH.This could be attributed to the impacts of age on the incidences of specific subtypes of lymphoid malignancies.For instance, ANKL patients, who frequently present with HLH, are mostly young to middle-aged adults. 12Intravascular large B-cell lymphoma (IVLBCL), another subtype that is associated with HLH, is more common in the elderly population. 13owever, as the distribution of lymphoma subtypes is different in different ethnic populations, for example, ANKL and ENKL is much more prevalent among Asians than in other populations, 14,15 our findings regarding the lymphoma subtypes may not apply to other populations.The prognosis of elderly patients with LA-HLH is poor, with a median survival of only 92 days.The difference in outcomes between elderly and young patients is not significant and this finding is observed in different subgroups (B-cell lymphoma or T/NK-cell lymphoma or Hodgkin lymphoma).The underlying reason for this phenomenon needs to be explored.The treatment for elderly patients with LA-HLH is challenging, as elderly lymphoma patients have more comorbidities and reduced tolerance to chemotherapies.The current treatment recommendation for LA-HLH is using HLH-directed therapy containing etoposide followed by lymphoma-directed therapy, which is also called a two-step approach. 16However, the role of HLHdirected therapy including the HLH-94 regimen in the treatment of LA-HLH remains controversial, primarily due to the lack of prospective randomized trials.A possible concern for the use of lymphoma-directed therapy is the intolerance of patients with HLH, as these patients always have poor performance status, severe cytopenia, and poor organ functions.The direct use of anti-lymphoma therapy may lead to increased therapyrelated mortalities.Previous studies suggested, that the use of etoposide, no matter in the HLH-directed or lymphoma-directed strategy, was associated with better outcomes. 17,18Our study did not show the use of HLH therapy or etoposide-containing HLH therapy was associated with improved outcomes.Additionally, the use of etoposide or etoposide-containing lymphoma therapy did not improve the OS of elderly patients with LA-HLH.These findings were not consistent with those from previous studies.However, in our study, for patients who received lymphoma-directed therapy, the use of etoposide-containing chemotherapy was associated with better 60-day survival.Interestingly, for elderly patients with B-cell LA-HLH, the use of etoposide or etoposide-containing lymphoma therapy was significantly associated with better 60-day survival but not OS.How to translate better 60-day survival into better OS needs to be explored in the future.Despite these findings, it should be mentioned that the selection of treatments for elderly patients with LA-HLH as well as etoposide doses need to be dependent on the organ functions and general conditions of these patients.
The poor prognosis of elderly patients with LA-HLH emphasizes an unmet need for therapeutic options of elderly patients with LA-HLH.For example, most of cases of IVLBCL, which is frequently associated with HLH, [19][20][21] are primarily MCD-type large B-cell lymphoma. 22As patients with MCD-type DLBCL may benefit from the addition of Bruton's tyrosine kinase inhibitors, 23 the use of Bruton's tyrosine kinase inhibitors could be promising in treating patients with IVLBCLassociated HLH.According to a phase 2 trial, all but one patient with IVLBCL who received zanubrutinib plus R-CHOP achieved complete response at the end of the therapy and no relapses occurred, suggesting this regimen is highly effective in patients with IVLBCL. 24Elderly patients with T/NK-cell LA-HLH had an even worse outcome and those with NK-cell lymphoid malignancy had a median overall survival of only 21 days.6][27] According to a retrospective study by He et al, the use of a combination of anti-PD-1 antibody plus chemotherapy seemed to be associated with prolonged survival in patients with ENKL-associated HLH. 28The efficacy and safety of the regimens containing anti-PD-1 or anti-PD-L1 antibodies in elderly patients with ENKL-associated HLH need to be confirmed in future prospective trials.Novel agents including JAK2 inhibitor ruxolitinib and the anti-IFN-γ monoclonal antibody emapalumab have shown promising effects in children with primary HLH. 29,30These agents may have a role in the treatment of elderly patients with LA-HLH, especially for those who do not tolerate routine therapy.
We analyzed the prognostic factors for elderly patients with LA-HLH.T/NK-cell subtype, lower platelet count, lower albumin level, higher LDH level, and higher creatinine were identified as independent factors for predicting poor prognosis for elderly patients with LA-HLH.The T/NK-cell subtype has been demonstrated as a negative predictor of survival in patients with LA-HLH, 5 as cases of the T/NK-cell type usually show a highly aggressive

F I G U R E 4
The OS (A) and 60-day survival (B) in elderly patients with lymphoma-associated hemophagocytic lymphohistiocytosis according to the prognostic index.OS, overall survival.
clinical course.Low platelet and increased creatinine have also been demonstrated as prognostic factors in patients with HLH. 31,32Low platelet counts and increased creatinine are associated with disease severity and indicate decreased tolerance to conventional therapy.By establishing a prognostic index comprising five factors, we categorized elderly patients into three groups and identified a group of patients at a very high risk of early death.The median survival for this group of patients was only 5 days.They are unlikely to tolerate routine therapies and novel treatments including emapalumab may be of potential efficacy in these patients.
Our study has limitations due to its retrospective nature.A precise diagnosis was not available for some cases in this cohort.For example, some cases could only be diagnosed as B-cell non-Hodgkin lymphoma or T cell lymphoma, not otherwise specified.The pathology of lymphoma was not centrally reviewed in this study.The baseline characteristics including performance status could affect the selection of treatments and could be confounding factors in analyzing the prognostic impacts of different treatments.However, this was not analyzed in the current study.Moreover, the patterns of treatment failures were not available.Prospective studies are warranted to address these limitations.
In conclusion, our study demonstrated that elderly patients with LA-HLH displayed different clinical characteristics and lymphoma subtypes from young patients.The prognosis of elderly patients with LA-HLH is poor, especially for those with T/NK-cell lymphoid malignancies, suggesting an unmet need in the treatment of elderly patients with LA-HLH.The initial use of HLH therapy or etoposide-containing HLH therapy was not associated with improved OS.Additionally, the use of etoposide, in HLH-directed or lymphoma-directed therapy, was not associated with improved OS.A five-point prognostic index could categorize elderly patients with LA-HLH into three groups with different survival outcomes.Future clinical trials are warranted to explore better therapeutic approaches for elderly patients with LA-HLH.

F I G U R E 1
The OS (A) and 60-day survival probabilities (B) of elderly (age >60 years) and young (age ≤60 years) patients with lymphoma-associated hemophagocytic lymphohistiocytosis.OS, overall survival.for this population.Although there is ongoing debate over the treatment strategy for patients with LA-HLH, we think that effective lymphoma-directed therapy is critical for improving the survival of patients with LA-HLH, especially long-term survival.The advent of novel agents may improve the outcomes of specific subgroups F I G U R E 2 The OS of elderly patients with lymphoma-associated HLH who received different patterns of treatments (A-D).HLH, hemophagocytic lymphohistiocytosis; OS, overall survival.F I G U R E 3The impact of pathological subtypes on OS of elderly patients with lymphoma-associated hemophagocytic lymphohistiocytosis.OS, overall survival.

Elderly patients Young patients p Value (N = 173) (N = 251)
; hemophagocytosis in bone marrow was present in 80.6% (133/165) of cases; 98.3% (169/172) and 94.8% (109/115) of cases showed hyperferritinemia and elevated soluble CD25; only 27 patients were evaluated for NK cell activity with 51.9% showing reduced NK cell activity.Persistent fever was less frequent in elderly patients.Absent or reduced NK cell activity was less frequent in elderly patients as compared with young patients, although the difference was not statistically significant.Elderly patients show significantly decreased albumin levels and increased creatinine levels, suggesting that organ functions were decreased in elderly patients.
T A B L E 2